how to separate more than 1 value in a text box with a semicolon in asp.net autocomplete textbox

I have a text box with auto complete extender and it works fine. How can I allow the user to enter more than 1 value by separting the first value with a semicolon(;)

<asp:TextBox ID="txt_to" runat="server" />

 <asp:AutoCompleteExtender ID="AutoC开发者_运维知识库ompleteExtender1" runat="server" TargetControlID="txt_to"
 MinimumPrefixLength="2" CompletionInterval="10" EnableCaching="true" FirstRowSelected="true" CompletionSetCount="3" UseContextKey="True" ServiceMethod="GetCompletionList" />

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As explained in the demo page here, you should use the DelimiterCharacters property:

<asp:AutoCompleteExtender ID="AutoCompleteExtender1" runat="server"
    TargetControlID="txt_to" MinimumPrefixLength="2" CompletionInterval="10"
    EnableCaching="true" FirstRowSelected="true" CompletionSetCount="3"
    UseContextKey="True" ServiceMethod="GetCompletionList"
    DelimiterCharacters=";" />